Conventional touch screen computing devices have been configured to identify the positioning and/or movement of one or more fingers or other objects on or near touch surfaces of the devices. For example, touch screens associated with some touch computing devices have been configured for receiving input via finger gestures and to perform one or more functions in response to those finger gestures. Certain touch screen computing devices can receive input from input devices such as stylus devices. A stylus is a writing, drawing, or pointing instrument or utensil that is generally configured to be hand held and, in the context of touch screen computing devices, used to interact with a touch surface. For example, touch screen computing devices have identified input based on one end of the stylus moving on or near the touch surface of the computing device. Styluses (or styli) have been used with personal digital assistant devices, tablet computing devices, smart phones, and other touch screen computing devices for handwriting, drawing, selecting icons, and providing other forms of input to such touch computing devices.
There are three general categories of stylus devices: active styli, pressure sensitive styli, and ‘dumb’ styli. Dumb styli have no internal electronic components, no batteries, and typically only have a capacitive rubber tip at an end of a pen-shaped body. Such styli are unable to detect amounts or levels of pressure applied via their tips onto a display of a touch computing device. Active styli are self-contained systems designed to work with specific, usually proprietary, touch computing devices. Active styli may include radios or other means to communicate with a particular touch device/platform and are typically limited to working with a proprietary touch screen interface of a closed, proprietary system. Such active styli are constrained to working with a given platform because other, third party touch computing platforms and devices will not recognize these closed-system styli as valid input devices.
In contrast to active styli, pressure sensitive styli are often designed to work with third party touch screens and touch computing devices not made by the manufacturer of such styli. Example pressure sensitive styli are described in more detail in U.S. patent application Ser. No. 13/572,231 entitled “Multifunctional Stylus”, filed Aug. 10, 2012, which is incorporated by reference herein in its entirety. The tips of pressure sensitive may include pressure-sensitive elements. Pressure sensitive styli seek to provide multiple levels of pressure sensitivity, which can be useful in drawing, graphics, and other touch-based applications. For example, pressure sensitive styli can be used to sketch a drawing and provide other touch inputs to applications such as Adobe® Ideas®, Adobe® Illustrator®, Adobe® Photoshop® Touch, and Adobe® Photoshop® executing on various touch computing devices and platforms such as tablet computing devices and smart phones.
Input devices that are capable of sensing or detecting more levels of pressure can be used to provide more types of controls, data, gestures, and other inputs to touch computing devices and touch-based applications. Such pressure sensitivity can be achieved via use of pressure sensitive tips and sensors. Prior solutions involved incorporating a number of complex moving parts and sensitive components into styli, making such styli susceptible to damage. The fragility of such input devices can decrease their reliability and durability, particularly in mobile environments.
Incorporating traditional pressure sensors into styli can require that styli tips and bodies be wider than traditional writing and drawing instruments, such as pens and pencils, which do not ergonomically enhance their use as styli and may cause discomfort during extended periods of use. Traditional techniques for detecting pressure or force are limited in terms of a number of levels of pressure sensitivity that can be detected. Such techniques limit the sensitivity of styli, thereby limiting the types of inputs and gestures styli can produce. Some techniques for sensing force or detecting levels of pressure include using sound pressure or a plastic disc as part of a stylus tip. Such techniques can disrupt a capacitive connection needed to interact with a touch surface, such as a capacitive touch screen, of a touch computing device.